The Autism Spectrum Disorders (ASD) encompass a spectrum of disorders which include autism,[unreadable] Pervasive Developmental Disorder - Not Otherwise Specified (PDD-NOS), Asperger"s disorder and Rett[unreadable] syndrome. The working hypothesis of this proposal is that individuals with ASD experience disturbances in the[unreadable] intricate interplay between genetic predisposition, environmental triggers and experience-mediated neuronal[unreadable] activity during a sensitive period of development, and that this leads to an altered program of gene expression.[unreadable] Thus the neurological disabilities that are characteristic of the disorder result from genetic variability in the[unreadable] processes of synaptic development, maturation, refinement, and connectivity that normally shape the brain, and[unreadable] from an environmental insult that perturbs normal experience-dependant synaptic development. This proposal[unreadable] offers a novel approach aimed at unraveling the genetic mechanisms, improving diagnosis, deciphering the[unreadable] interplay between environment and genetics, and developing rational approaches to therapy.